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3

One disadvantage of DSA as conventionally implemented is that the key can be compromised if signatures are created on machines with poor random number generators. In the wake of the Debian openssl fiasco this meant that any DSA key that had been used in an openssh client on an affected machine was potentially compromised. With RSA keys only keys generated ...

2

If attackers can strip off RSA / EC / -DSA digital signature and conduct CCA on AES-CTR or CBC payload, why can't they do the same for AES-GCM? The scenario, you're talking about is iMessage or Signal Protocol or other protocols which allow optionally to sign the ciphertext and thereby don't MAC it. The problem here is a) that you could replace the ...

0

The problem with non-authenticated symmetric cipher modes is that they are PRP's. That means that - no matter what you do to the ciphertext - you'll get a valid and unique plaintext (not considering unpadding). This means that an attacker can change (part of) the outcome of decryption by altering the ciphertext. It can also lead to information leakage, e.g. ...

2

No, you do not add the ASN.1 encoding to the hash when generating an ECDSA signature. There are two reasons for this: The first is that there is no room, if we select a curve and a hash with equal security. To be secure against attacks that take $O(2^N)$ time, a curve needs to have a prime that's at least $2N$ bits; to be secure against collision attacks ...

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